A power distribution network loop closing power supply method based on multi-terminal electromagnetic interconnection device

Abstract

This invention discloses a method for loop-connected power transfer in distribution networks based on multi-terminal electromagnetic interconnection devices, belonging to the field of distribution network operation control and uninterrupted power transfer technology. The method first establishes an equivalent model of the multi-terminal electromagnetic interconnection device topology, using the equivalent voltage established by the excitation end line through the device as the intermediate voltage source for loop-connected power transfer; it then decomposes the loop current and constructs a calculation formula for the loop current. Next, a discrete compensation voltage vector diagram is established, and tap selection is completed based on the principle of minimum distance between the target compensation voltage and discrete tap voltage points. Subsequently, candidate switch sequence schemes are constructed, forming a comprehensive evaluation system. Each candidate scheme is verified by tap matching, power transfer, and power transfer completion criteria to obtain a comprehensive evaluation value, select the optimal switch sequence, and complete smooth power transfer. This method provides clear analytical calculation basis, tap selection basis, and sequence optimization basis for multi-terminal electromagnetic interconnection devices participating in uninterrupted loop-connected power transfer in distribution networks.

Description

Technical Field

[0001] This invention relates to the field of power distribution network operation control and uninterrupted power supply technology, and in particular to a power distribution network loop transfer method based on a multi-terminal electromagnetic interconnection device. Background Technology

[0002] During the operation of medium-voltage distribution networks, when line faults occur, planned maintenance is carried out, loads are transferred, or power supply methods are adjusted, it is usually necessary to transfer loads originally powered by one source to other lines to ensure uninterrupted or minimally interrupted power supply. Existing projects often use tie switches to achieve load transfer in the distribution network. However, due to the common voltage amplitude differences, phase angle differences, and impedance differences between the lines to be tied, a large closing current can easily be generated at the moment the tie switch closes, leading to problems such as switch contact impact, voltage fluctuations, protection malfunctions, and even equipment overheating.

[0003] Traditional loop-connection power transfer methods are mainly based on the direct rigid parallel connection of two feeders. The core of its control is to minimize the voltage difference on both sides of the loop to be connected, and to complete the load transfer by relying on the natural redistribution of power flow in the system or by supporting voltage regulation methods after the loop is closed. However, in scenarios where multiple lines are involved in power transfer, power transfer needs to be completed in stages, or flexible power exchange needs to be achieved under electrical isolation conditions, the direct loop-connection method is difficult to balance loop current suppression, power supply continuity, and power flow controllability.

[0004] In recent years, interconnection devices, phase-shifting compensation devices, and multi-terminal electromagnetic interconnection devices based on the principle of electromagnetic coupling have provided new technical pathways for uninterrupted power transfer in distribution networks. These devices can establish a magnetic flux within the excitation-side winding and then induce an adjustable compensation voltage through the target-side winding, thereby achieving voltage matching and power exchange without directly and rigidly paralleling the power sources on both sides. Especially in scenarios where a main power supply line needs to sequentially transfer loads to two target lines, a single multi-terminal electromagnetic interconnection device can achieve multi-port energy coupling and compensation regulation within the device itself, offering advantages such as compact structure, flexible power transfer, and minimal modification to the original system.

[0005] However, existing technologies still lack a systematic loop-connection and transfer method for such multi-terminal electromagnetic interconnection devices. First, for scenarios where a single device connects three lines A, B, and C, there is a lack of an approximate calculation method for the loop-connection current that matches its operating mechanism, making it difficult to quickly estimate the loop-connection impact at each stage before operation. Second, these devices typically use tap-based voltage regulation to change the compensation voltage, but the actual compensation voltage points are discretely distributed. Existing technologies lack a unified quantitative criterion for selecting the appropriate tap based on the target voltage difference. Third, when multiple switching sequences exist, improper sequence selection can easily lead to problems such as simultaneous supply of three power sources, voltage mismatch at intermediate nodes, excessive loop-connection current, and unstable load transfer. Therefore, a quantifiable and comparable sequence evaluation system is needed.

[0006] Therefore, how to establish a modeling method, tap selection method, power transfer method, and switching sequence optimization method for a single multi-terminal electromagnetic interconnection device to achieve smooth load transfer in the distribution network while ensuring voltage quality and equipment safety has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a method for loop-connecting power transfer in a distribution network based on a multi-terminal electromagnetic interconnection device, in order to solve the problems in the prior art where there is no unified calculation basis for loop-connecting current, no clear mechanism for tap selection, no formalized power regulation method for the power transfer process, and no quantitative optimization basis for switching sequence in multi-terminal electromagnetic interconnection scenarios.

[0008] To achieve the above objectives, this invention proposes a method for loop-connecting power supply in a distribution network based on a multi-terminal electromagnetic interconnection device. The multi-terminal electromagnetic interconnection device is connected to line A, line B, and line C respectively, and includes the following steps: (1) Establish a topology model of a multi-terminal electromagnetic interconnection device consisting of line A, line B and line C, and use the equivalent voltage established at point O by the excitation end line through the electromagnetic interconnection device as the intermediate equivalent power supply for the target line loop transfer.

[0009] (2) Establish a closed-loop equivalent impedance model for the target line and calculate the closed-loop current. The closed-loop current is obtained by superimposing the closed-loop current component caused by voltage difference and the closed-loop current component caused by load transfer.

[0010] (3) Establish a discrete compensation voltage vector diagram formed by the combination of secondary winding taps, and select the optimal tap position according to the Euclidean distance between the target compensation voltage and each discrete compensation voltage point.

[0011] (4) Construct candidate switch sequence schemes for the line, and perform tap position matching, loop current prediction, power transfer and load transfer calculations on the candidate switch sequence schemes to obtain the evaluation results of each candidate switch sequence scheme.

[0012] (5) Establish a comprehensive evaluation index based on the maximum loop closing current, the total current stress of each major loop closing process and the maximum voltage deviation of the whole process, and select the switching action sequence with the best comprehensive evaluation index as the optimal switching sequence.

[0013] (6) Perform the target line loop closing, power transfer and original power supply disconnection operations in the optimal switching sequence to complete the distribution network loop closing and power transfer.

[0014] The multi-terminal electromagnetic interconnection device is a single three-terminal electromagnetic interconnection device, comprising one primary winding and two secondary windings arranged on the same magnetic circuit, namely the first winding, the second winding, and the third winding. The first winding is connected to line A, and the two secondary windings, the second winding and the third winding, are connected to lines B and C, respectively. Adjustable taps are provided in the first winding and the two secondary windings to change the equivalent turns ratio, compensation voltage amplitude, and compensation voltage phase angle of the device.

[0015] This invention first models the closed-loop topology involving a multi-terminal electromagnetic interconnection device. When line A is the excitation side, a magnetic flux is established in the common magnetic circuit through the first winding of line A, forming an equivalent compensation voltage facing line B or line C on the secondary side. For ease of analysis, the common coupling node inside the device is abstracted as point O, and the equivalent voltage established at point O by the device on the excitation side is used as the intermediate equivalent voltage source for the closed-loop transfer of the target line. Based on this, a closed-loop equivalent impedance model is constructed for the target line, and an approximate formula method is used to decompose the closed-loop current into the closed-loop current component caused by voltage difference and the closed-loop current component caused by load transfer, thereby obtaining a closed-loop current calculation expression applicable to multi-terminal electromagnetic interconnection devices.

[0016] Furthermore, this invention establishes a tap selection mechanism. Since changes in winding taps can only create a finite number of discrete compensation voltage points, the compensation voltages corresponding to all tap combinations are represented as a discrete compensation voltage vector diagram. Based on the difference between the voltage at the target loop point and the equivalent voltage at point O, the target compensation voltage is calculated. Then, using the principle of minimum distance between the target compensation voltage and each discrete compensation voltage point, the tap position closest to the target compensation voltage is selected, thereby achieving joint matching of the compensation voltage amplitude and phase angle.

[0017] Regarding the switching sequence, this invention, based on the connection relationship between the three lines and point O, eliminates unfavorable sequences that could lead to simultaneous power supply from all three power sources, retaining four candidate sequence schemes: ABC, ACB, BAC, and CAB. Specifically, ABC indicates that the equivalent voltage at point O is established first from side A, with priority given to transferring power from side B, followed by transferring power from side C; ACB indicates that the equivalent voltage at point O is established first from side A, with priority given to transferring power from side C, followed by transferring power from side B; BAC and CAB respectively indicate that the initial equivalent voltage at point O is established from side B or side C through reverse excitation, and then the connection and transfer of power to the remaining lines are completed according to a preset sequence.

[0018] This invention also proposes a formalized power regulation mechanism for the power transfer process. Once a target line has been connected to point O via a switch, the amplitude and phase angle differences between the equivalent voltages on both sides are changed by jointly adjusting the taps of the primary winding and the corresponding secondary winding on the target side, causing active and reactive power to flow between the two sides in the expected direction. Specifically, active power transfer is controlled by adjusting the phase angle difference of the equivalent voltage, and reactive power and voltage support are controlled by adjusting the amplitude difference of the equivalent voltage, thereby gradually and smoothly transferring the load of the target line from the original power supply to the preferred power supply.

[0019] To achieve a unified comparison of the four candidate schemes, this invention establishes a multi-index evaluation system, including three indicators: the maximum loop current throughout the entire process, the total current stress of each major loop closing process, and the maximum voltage deviation throughout the entire process. After normalizing each indicator, a comprehensive evaluation value is constructed, and the optimal switching sequence is automatically selected from the four candidate schemes based on the principle of minimizing the comprehensive evaluation value.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: First, this invention establishes an approximate calculation method for the loop current of a single multi-terminal electromagnetic interconnection device, enabling rapid estimation of the loop current magnitude at different stages before operation. Second, this invention proposes a nearest-neighbor tap selection mechanism applicable to discrete tap compensation voltage and introduces a diamond-shaped region division to reduce computational load, providing a clear quantitative basis for tap selection. Third, this invention formalizes the power transfer process into a joint adjustment process based on the equivalent voltage amplitude difference and phase angle difference, making the load transfer mechanism clearer and more controllable. It also introduces a dynamic load transfer ratio coefficient, which can reflect the load transfer progress in real time and be used for current prediction before loop closure, avoiding inrush current. Fourth, this invention establishes a unified evaluation system for four candidate order schemes, which can automatically select the optimal scheme by comprehensively considering equipment current inrush, total stress, and voltage quality, enhancing the engineering applicability and safety of the method. Attached Figure Description

[0021] Figure 1This is an overall flowchart of the distribution network loop transfer method based on a multi-terminal electromagnetic interconnection device according to the present invention.

[0022] Figure 2 This is a schematic diagram of the topology of a single multi-terminal electromagnetic interconnection device connecting lines A, B, and C in this invention.

[0023] Figure 3 To be Figure 1 The topology shown is an equivalent topology graph with point O as the core node.

[0024] Figure 4 A schematic diagram showing the ideal adjustable range of the compensation voltage and the distribution of discrete tap compensation points.

[0025] Figure 5 A schematic diagram illustrating the principle of nearest neighbor selection between the target compensation voltage and the candidate tap voltage point. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0027] I. Device Structure and Equivalent Topology

[0028] The multi-terminal electromagnetic interconnection device involved in this embodiment is a single three-terminal electromagnetic interconnection device. This device includes one primary winding and two secondary windings arranged on the same magnetic circuit, namely a first winding, a second winding, and a third winding. The first winding is connected to line A, the second winding to line B, and the third winding to line C. At least a portion of the primary winding and the two secondary windings are provided with adjustable taps for adjusting the equivalent turns ratio of the device and the output compensation voltage by changing the effective number of turns of the winding. Figure 2 As shown, the device is connected to line A, line B and line C respectively. , , These represent the common terminal voltages of the secondary windings a1, b1, and c1 of a multi-terminal electromagnetic interconnection device. In a typical wiring configuration, , , Normally, when grounded or connected to the neutral point, its voltage is zero. Aa U Ab and U Ac These are the three-phase voltages of line A, U Ba U Bb and U Bc These are the three-phase voltages of line B, U Ca U Cb and U Cc These are the three-phase voltages of line C. L AFor the load on side A of line, L B For the load on the B side of the line, L C This is the load on the C side of the line.

[0029] When line A is used as the excitation side, the voltage of line A establishes a magnetic flux in the common magnetic circuit through the first winding, and induces compensation voltages in the second and third windings respectively. For ease of analysis, the voltage coupling result inside the device is abstracted as the equivalent voltage at point O. That is, the multi-terminal electromagnetic interconnection device is equivalent to: line A establishes an adjustable equivalent voltage source at point O through the device, and lines B and C are connected to point O through their respective ports.

[0030] like Figure 3 As shown, in the equivalent topology, switch K A K B K C These represent the connection switches between line A, line B, and line C and point O, respectively. UA is the three-phase voltage vector of line A, UB is the three-phase voltage vector of line B, and UC is the three-phase voltage vector of line C. The connection between line A and point O is mainly used to establish voltage at point O, while the connections between line B and line C and point O are mainly used for connection, loop closing, and subsequent load transfer under voltage matching conditions.

[0031] II. Calculation Method for Closed-Loop Current

[0032] When the target line is line B, the equivalent voltage facing line B established at point O from line A via the multi-terminal electromagnetic interconnection device can be expressed as:

[0033] Among them, U A Let T be the three-phase voltage vector of line A. AB The equivalent transformation relationship from A to B is determined by the winding coupling relationship, the effective number of turns in each winding, and the current tap position. This equivalent transformation relationship can be determined based on the device's factory parameters, the winding turns ratio, and the turns ratio corresponding to the tap position. For example, when the tap positions on sides A and B change, their effective turns ratio changes accordingly, thereby causing T... AB The corresponding changes in amplitude and phase. U O (B) Let O be the equivalent voltage vector facing line B.

[0034] Specifically, under an equivalent condition, let the effective number of turns of the winding on line A and the winding on line B at the current tap position be N respectively. A,eff and N B,eff The equivalent coupling coefficient between the A and B windings is k. AB The equivalent phase shift angle is θ AB Then the equivalent transformation relationship can be expressed as:

[0035] Where the rated number of turns on side A and side B of line A are N A0 and N B0 The corresponding tap positions are s A and s B The change in the number of turns for each gear is ΔN. A and ΔN B Then there is

[0036] Therefore, changing the tap position will further change T by altering the effective turns ratio. AB The amplitude; when the device has phase compensation, the coupling relationship and wiring method can also jointly affect θ. AB This causes T AB Phase change. For example, when N A0 =1000 turns, N B0 =800, tap A is in the +2nd position and tap B is in the -1st position, the number of turns for each position changes by 10 turns, and k AB =0.98, θ AB When =5°, then

[0037] Furthermore,

[0038] Explanation T AB It can be specifically determined by parameters such as the number of winding turns, tap position, and coupling coefficient.

[0039] Similarly, when the target line is line C, we have:

[0040] Among them, T AC For the equivalent transformation relationship from A to C, U O (C) Let O be the equivalent voltage vector facing line C.

[0041] When the target line X is line B, the three-phase compensation voltages satisfy the following: ; ; ; in, , , These are the tap voltages of the secondary windings a1, b1, and c1 of the multi-terminal electromagnetic interconnection device, respectively. Their amplitude and phase change with the position of the corresponding winding taps. When the target line X is line C, the three-phase compensation voltage uses the same expression as line B, that is: ; ; .

[0042] For any target line X (X can be B or C), any phase The closed-loop current can be expressed by an approximate formula as follows:

[0043] Among them, I 0,X, I is the closed-loop current component caused by the difference between the equivalent voltage at point O and the original voltage of the target line. s,X, This refers to the closed-loop current component caused by the load transfer of the target line.

[0044] The closed-loop current component caused by the voltage difference is expressed as:

[0045] In the formula, U O, (X) For point O facing the target line X Equivalent voltage, U X, For the target line X The original voltage of phase Z AO, Z is the equivalent impedance of the path from line A through the device to point O. OX, It is the equivalent impedance from point O to the target line access point.

[0046] The closed-loop current component caused by load transfer is expressed as:

[0047] In the formula, λ X, S is the load transfer ratio coefficient for the target line. LX, For the target line X Phase load power λ represents the conjugate operation. X, The value of λ ranges from 0 to 1, and the initial state is λ. X, =0 indicates that the load is entirely powered by the original power source. As the target line load gradually shifts from the original power source to the preferred power source, λ X, Gradually increase, λ after the transfer is completed X, =1 indicates that the entire load has been transferred to the target power source.

[0048] Therefore, the total loop current of the target line can be expressed as:

[0049] The above expression reflects two main influencing factors: firstly, the degree of mismatch between the equivalent voltage at point O and the original voltage of the target line; and secondly, the additional current change caused by the load on the target line during the transfer process. This formula allows for prediction of the initial loop current before the switch is closed, and also for estimation of the current levels at each stage during the transfer process.

[0050] III. Tap Selection Mechanism

[0051] To reduce the voltage difference before loop closure, an appropriate tap needs to be selected based on the difference between the equivalent voltage at point O and the target line voltage. Since the winding tap positions are discrete, the actual compensating voltage that can be formed is also discretely distributed, with each discrete point corresponding to a candidate tap voltage. For example... Figure 5 As shown, this invention performs nearest neighbor matching between the target compensation voltage and the discrete compensation voltage points, and selects the optimal tap based on the principle of minimum Euclidean distance.

[0052] Let the set of all discrete compensation voltage points formed by tap combinations be:

[0053] Where N is the number of discrete points of the compensation voltage, which depends on the number of windings involved in the adjustment, the number of taps in each winding, and the tap combination method.

[0054] Specifically, let there be m windings participating in the compensation adjustment, i.e., windings with adjustable taps, and the i-th winding is at the current tap position s. i The effective number of turns is denoted as N. i,eff (s i Based on the relationship that the induced electromotive force is proportional to the effective number of turns of the winding, and assuming the common magnetic flux remains approximately constant, taking single-phase analysis as an example, let the voltage of a certain phase of line A be... The i-th winding is at this tap position The corresponding compensation voltage component can be expressed as: For different phases, similar expressions can be established. Where k i N is the equivalent coupling coefficient between the i-th winding and the first winding on the excitation side.A,eff This represents the effective number of turns of the first winding on the excitation side at the current tap position. i Let N be the phase direction of the compensation voltage component for the i-th winding. If the rated number of turns for the i-th winding is N... i0 The change in the number of turns corresponding to each tap is ΔN. i Then we have: Where si is an integer, a positive value indicates an increase in the number of turns, a negative value indicates a decrease in the number of turns, and zero indicates the base position. For any set of tap combinations τ=(s1,s2,…,s…) m The corresponding discrete compensation voltage point is obtained by superimposing the compensation voltage component vectors of each winding, that is: The set of discrete compensation voltage points formed by all feasible tap combinations can be expressed as: Where Γ is the set of all feasible tap combinations, and N is the total number of discrete compensation voltage points after removing duplicate voltage points. If the number of tap positions (including the reference position) of the i-th winding is n... i The total number of tap combinations is When the compensation voltage points corresponding to different tap combinations do not coincide, N = M; when some tap combinations correspond to the same compensation voltage point, N <M。

[0055] In one typical implementation, when each winding has a center tap, it can be formed as follows: Figure 4 The figure shows 18 peripheral compensation points plus 1 central reference point, totaling 19 typical discrete points. The peripheral compensation points are represented by serial numbers 1-18 in the figure, but the present invention is not limited to 19 discrete points.

[0056] Based on the difference between the voltage at the target loop point to be closed and the equivalent voltage at point O, the target compensation voltage vector is obtained:

[0057] Among them, U X U is the voltage vector at the point where the loop to be closed in the target line. O (X) This is the equivalent voltage vector from point O towards the target line.

[0058] The target compensation voltage is expressed in planar coordinate form:

[0059] Let the discrete compensation voltage point corresponding to the k-th tap combination be:

[0060] The distance between the target compensation voltage and the discrete compensation voltage point of the tap is defined as:

[0061] According to the minimum distance principle, the optimal tap position satisfies:

[0062] That is, the tap combination that minimizes the distance between the target compensation voltage and the actual discrete compensation voltage point is selected as the current optimal tap.

[0063] In one preferred implementation, the two winding taps involved in the compensation adjustment can be denoted as indices p and q, respectively. For any pair of adjacent tap combinations (p, q), (p+1, q), (p, q+1), (p+1, q+1), the four discrete compensation voltage points corresponding to these combinations form a local quadrilateral region on the complex plane. When this quadrilateral exhibits a rhomboid distribution or is approximately a rhomboid region, it can be defined as a rhomboid region. For example... Figure 4 As shown, multiple rhomboid regions can be formed by connecting discrete compensation voltage points according to the tap index. When the target compensation voltage falls into a certain rhomboid region, it is only necessary to compare the local minimum distance between the adjacent tap points corresponding to the vertex of the region to obtain the optimal tap, thereby reducing the amount of online calculation.

[0064] IV. Construction of Candidate Switch Sequence Scheme

[0065] When three lines are connected in stages via a single multi-terminal electromagnetic interconnection device, improper operation sequence can easily lead to simultaneous power supply from three power sources. To avoid this, this implementation first eliminates the unfavorable sequences CBA and BCA, retaining the following four candidate sequence schemes: S1: ABC; S2: ACB; S3: BAC; S4: CAB.

[0066] Wherein, S1 means that the equivalent voltage is first established at point O by line A through the first winding, then the loop closing and power transfer of line B are completed first, and then the loop closing and power transfer of line C are completed; S2 means that the voltage is first established by line A, the loop closing and power transfer of line C are completed first, and then the power transfer of line B is completed.

[0067] For S3 and S4, since the device's structure is "primary side connected to line A, and two secondary sides connected to lines B and C respectively," a reverse excitation mode is used when B or C is the initial voltage-building side. That is, line B or line C temporarily provides excitation to the common magnetic circuit through the corresponding secondary winding, establishing an initial equivalent voltage at point O. After subsequent line connections and power adjustments are completed, the power transfer is completed according to the predetermined target. This reverse excitation does not change the physical structure of the device; it only changes the initial excitation direction and the initial energy input terminal.

[0068] V. Specific Operational Procedures for Scheme S1

[0069] The operation process of this invention will be described in detail below using S1 scheme as an example. The goal of S1 scheme is to first complete the load L on the B side of the line. B The power is transferred to line A, and then the load L on the line C side is completed. C The transfer of power to line A is ultimately transferred from line A to the load L on line B. B and load L on line C side C powered by. Figure 1 The overall flowchart of the method of the present invention is shown below, in conjunction with... Figure 1 Each step is described in detail.

[0070] First, a topology model of a multi-terminal electromagnetic interconnection device consisting of lines A, B, and C is established. The equivalent voltage established at point O through the electromagnetic interconnection device on the excitation-end lines is used as the intermediate equivalent power source for the target line's loop-connection power supply. Then, a loop-connection current calculation method is established, a tap selection mechanism is constructed, and a candidate switch sequence is built. Next, each candidate scheme is calculated and adjusted, a comprehensive evaluation index is established, the optimal sequence is selected, and finally, the loop-connection power supply is executed. The following uses scheme S1 as an example to explain each step in detail.

[0071] In the initial state, line B and line C are powered by their respective original power sources, K A K B K C All are disconnected. First, close K. A An equivalent voltage is established at point O via line A and the first winding:

[0072] Among them, T A For the first winding tap position, G A (T A ) represents the equivalent transformation relationship under the corresponding tap.

[0073] This stage does not require the voltage at point O to immediately match that of line B perfectly. Instead, a coarse adjustment of the current transformer (CT) is performed first to ensure that the voltage at point O falls within the compensable range of line B, thus reserving a better matching margin for the initial connection to line B. The objective of this coarse adjustment can be written as:

[0074] Among them, H B For the matched area covered by the discrete compensation voltage on side B of the line, d( H B () represents the distance from a point to a region.

[0075] Once the voltage at point O is established, the tap position of the second winding is selected based on the difference between the current voltage at point O and the equivalent voltage on the B side of the line. Let U be the equivalent voltage at point O corresponding to the k-th tap on the B side of the line. B→O,k Then we have:

[0076] Take the satisfaction

[0077] The tap is used as the optimal tap when line B connects to point O.

[0078] In closed K B Beforehand, the first loop current needs to be predicted using the aforementioned loop current calculation method. This can be written as:

[0079] Among them, Z loop,B λ is the closed-loop equivalent impedance when line B is connected. B (0) This represents the initial transfer ratio during the initial access phase, typically a smaller value. In one embodiment, the initial transfer ratio λ during the initial access phase... B (0) A smaller value can be selected, such as 0.05 to 0.20, to reduce the inrush current during the first loop closure.

[0080] When |I h,B cl | When the limit is not exceeded, close switch K. B This connects line B to point O and puts it into a temporary parallel state. The upper limit of the allowable loop current can be set comprehensively based on the protection settings, the thermal stability current of the equipment, the rated current carrying capacity of the switch, and the maximum loop current allowed by the dispatching procedures.

[0081] In one preferred embodiment, the following may be taken:

[0082] Where Iprot is the current limit corresponding to the protection action constraint, Ith is the allowable current for equipment thermal stability, and Ireg is the maximum closed-loop current allowed by the dispatching procedure. To improve the safety margin, the actual criterion can be further corrected using a safety factor η, that is, when the predicted closed-loop current meets the requirements... The switch is allowed to be closed at a certain time, where η can be 0.80 to 0.95.

[0083] In K A and K B After both circuits are closed, line A and line B establish a temporary coupled power exchange channel through the multi-terminal electromagnetic interconnection device and point O. At this time, it is necessary to adjust the primary side tap and the second winding tap to adjust the load L.B The power supply will be gradually switched from line B to line A.

[0084] Let the equivalent voltage on line A and the equivalent voltage on line B after transformation by the device be as follows:

[0085] Among them, T A and T B These are the tap positions of the first and second windings of the multi-terminal electromagnetic interconnection device, respectively. Define the phase angle difference of the equivalent voltages on both sides of line A and line B as:

[0086] in, Let be the phase angle of the equivalent voltage on side A of the line. The phase angle is the equivalent voltage on side B of the line.

[0087] The equivalent reactance of channel AB is X. AB Under approximate conditions, the active power from line A to line B and reactive power They respectively satisfy:

[0088] The above relationship shows that by adjusting δ AB The direction and magnitude of active power transmission from A to B can be changed; the reactive power distribution and voltage support level can be altered by adjusting the difference in equivalent voltage amplitude between the two sides. Therefore, adjusting the taps on the primary side and B side makes L... B Powered by line A, its essence is to adjust the taps on the primary and second windings by changing the circuit. and The phase angle difference and amplitude difference cause line A to provide more and more active power and appropriate reactive power to line B until the output of line B at the source end drops to near zero.

[0089] For the power transfer of line C, let the equivalent voltage on side A and the equivalent voltage on side C after transformation by the multi-terminal electromagnetic interconnection device be respectively:

[0090] Among them, T A and T C These are the tap positions of the first and third windings of the multi-terminal electromagnetic interconnection device, respectively. The phase angle difference between the equivalent voltages on both sides of line A and line C is: ;in, Let be the phase angle of the equivalent voltage on side A of the line. The phase angle is the equivalent voltage on side C of the line; The equivalent reactance of the AC channel is X. AC Under the condition of [condition], the active power transferred from line A to line C and reactive power Approximately satisfies: ; ; This achieves the load L of line C. C The power supply is smoothly transferred from the original power source of line C to line A.

[0091] To facilitate engineering implementation, the joint adjustment of taps in this stage can be written as an optimization objective function:

[0092] Among them, P SB and Q SB These represent the active and reactive power outputs of the original power supply source for line B, respectively, Q. SB ref For reference reactive power, N B For the set of key monitoring nodes on side B of the line, α P α Q α U This refers to the weighting coefficient α. P α Q α U It can be set according to the operational control objectives; when priority is given to the smooth shutdown of the original power supply, α can be appropriately increased. P When voltage quality is a priority, α can be appropriately increased. U In one embodiment, α can be taken. P ≥α U ≥α Q For example, α can be taken. P =0.5、α Q =0.2、α U =0.3. By selecting from the candidate tap combinations, J... AB The smallest tap pair can achieve L B Smooth supply transfer. Among them, The actual voltage at node n; Let N be the reference voltage for node n. The set of key monitoring nodes can be selected according to the distribution network topology, and typically includes bus voltage monitoring points on both sides of the loop closure point, important load connection points, and the original power supply outlet. For the set of key monitoring nodes N on line B... BThe specific nodes can be determined based on the actual feeder structure and load distribution of line B; for the set of key monitoring nodes N throughout the entire process, the union of all nodes that may be affected by the transfer process under each candidate scheme can be selected.

[0093] The load L on the B side of line is determined when any of the following sets of conditions are met. B The transfer of power from the original power source of line B to line A has been completed:

[0094] The load L of line C is determined when at least one of the following conditions is met at the original power supply outlet of line C. C The transfer of power from the original power source of line C to line A has been completed:

[0095] Where, ε P ε I ε U These are the allowable power, current, and voltage deviation thresholds, respectively, P SC and I SC These represent the output power and current of the original power supply for line C, and N. C This refers to the set of key monitoring nodes on the C side of the line. The allowable power, current, and voltage deviation thresholds can be set according to the distribution network operation regulations, protection setting requirements, and equipment rated parameters. In a preferred embodiment, the power deviation threshold ε can be... P Set the current deviation threshold ε to 1% to 5% of the rated power of the original power supply for line B or line C. I Set the voltage deviation threshold ε to 1% to 5% of the corresponding rated current. U Set to 0.5% to 2% of the node's rated voltage. For example, it can be taken as: Among them, P N I N and U N These are the rated power, rated current, and rated voltage of the corresponding equipment or node.

[0096] Once the above conditions are met, disconnect the original power supply switch for line B. At this time, the load L... B Power is supplied from line A via a multi-terminal electromagnetic interconnection device.

[0097] After the original power supply for line B is disconnected, the system is no longer in a three-power supply state. Subsequently, the connection and transfer of power to line C are completed following the same approach as for line B. Specifically, the third winding tap is selected based on the difference between the current voltage at point O and the equivalent voltage on the line C side, and K is closed under the condition that the predicted loop current meets the limit. CThe method for determining the upper limit of the allowable loop current is the same as when line B is connected, and will not be repeated here. Then, by jointly adjusting the primary side tap and the line C side tap, L... C The power supply will be gradually switched from the original power source of line C to the power source of line A.

[0098] Once the original power supply output of line C meets the corresponding threshold conditions, the original power supply switch for line C is disconnected, thus completing the load transfer on the line C side. At this point, the S1 scheme is complete, and the final state is that line A simultaneously supplies power to line L. B and L C powered by.

[0099] VI. Explanation of S2, S3 and S4 schemes

[0100] Scheme S2 shares the same overall approach as Scheme S1, the only difference being that the transfer of power from line C to line B is completed first. That is, the equivalent voltage at point O is established first by line A, then line C is connected first to complete the transfer of power from LC to line A. After the original power source of line C is disconnected, line B is connected and the transfer of power from LB to line A is completed.

[0101] In scheme S3, line B reverses the common magnetic circuit of the device through its corresponding second winding, establishing an initial equivalent voltage at point O. Then, it connects to line A according to a predetermined rule, and further connects to line C, ultimately achieving the transfer of the target load in a predetermined direction. Although the initial excitation side is provided by line B, the device's main structure remains a single primary side plus two secondary sides; only the operating state changes.

[0102] In S4, line C reverse-excites the common magnetic circuit through its corresponding third winding, establishing an initial equivalent voltage at point O; then it connects to line A, then to line B, completing the corresponding load transfer. The tap selection, loop current prediction, and power transfer principles of S3 and S4 are the same as those of S1, only the initial excitation terminal and subsequent connection sequence are different.

[0103] VII. Evaluation of the Four Schemes and Selection of the Optimal Order

[0104] To select the optimal switching sequence from the four candidate schemes S1, S2, S3 and S4, this implementation establishes the following three evaluation indicators.

[0105] The first indicator is the maximum loop current throughout the entire process:

[0106] Where m represents the candidate scheme number, and T is the total time of the scheme. This indicator is used to reflect the maximum current surge level throughout the entire process of the scheme.

[0107] The second indicator is the total current stress during each major loop-closing process:

[0108] Where, N h The number of main loop-closing processes is typically taken as 2 in this embodiment, corresponding to two main line access processes. Tr1 represents the number of major loop closure processes, and [tr1, tr2] represents the duration of the transient state of the r-th major loop closure. This index is used to reflect the cumulative thermal and electrodynamic stresses throughout the entire process.

[0109] The third indicator is the maximum voltage deviation throughout the entire process:

[0110] Where N is the set of key monitoring nodes throughout the entire process, U n ref This is the reference voltage for the corresponding node n. This indicator is used to reflect the worst level of power quality during the power transfer process.

[0111] The three indicators above are normalized by range to obtain J1. ,m J 2,m and J3 ,m And construct a comprehensive evaluation value:

[0112] Where ω1, ω2, and ω3 are weighting coefficients, satisfying:

[0113] In a set of recommended embodiments, the following may be adopted: The reasons are as follows: the maximum loop current throughout the entire process directly affects switch safety and equipment impact, and should be given a higher weight; the total current stress reflects the cumulative thermal stress and electrodynamic effects; and the maximum voltage deviation reflects the power supply quality, so the two can be given similar weights. For scenarios with a high proportion of voltage-sensitive loads, the value of ω3 can also be appropriately increased.

[0114] After performing loop current calculations, tap matching, power transfer process simulations, or online estimations on the four candidate schemes, four sets of evaluation results can be obtained: FS1, FS2, FS3, and FS4. The optimal switching sequence is determined by the following formula:

[0115] The candidate solution with the lowest overall evaluation value is selected as the final implementation solution.

[0116] Therefore, the results of the four schemes obtained in this invention, and the specific meaning of selecting the optimal switching sequence according to the evaluation system, are as follows: the tap sequence, loop current process, voltage deviation process and comprehensive evaluation value of the four schemes S1, S2, S3 and S4 are obtained respectively, and the optimal scheme is automatically selected accordingly, rather than a certain sequence is fixed in advance.

[0117] VIII. Final Output and Application Method

[0118] After using the method of this invention, the following results can be output: First, the calculation results of the loop current of each target line at different stages; second, the optimal tap position and its corresponding compensation voltage at each stage; third, the maximum loop current, total current stress and maximum voltage deviation of the four candidate sequence schemes; fourth, the comprehensive evaluation value of the four candidate sequence schemes; and fifth, the final determined optimal switching sequence and corresponding transfer path.

[0119] The above results can be used to formulate power transfer plans offline, or to achieve online or quasi-online decision-making in conjunction with distribution automation systems. For different line capacities, load levels, and impedance parameters, this invention can achieve rapid pre-operation evaluation and sequential optimization using the same modeling framework.

[0120] The above are merely preferred embodiments of the present invention. For those skilled in the art, various modifications, substitutions, and improvements can be made without departing from the spirit and essence of the present invention, and all such modifications, substitutions, and improvements should fall within the protection scope of the present invention.

Claims

1. A method for loop-connecting power supply in a distribution network based on a multi-terminal electromagnetic interconnection device, wherein the multi-terminal electromagnetic interconnection device is respectively connected to line A, line B, and line C, characterized in that, Includes the following steps: A topology model of a multi-terminal electromagnetic interconnection device consisting of three lines, A, B and C, is established. The equivalent voltage established at point O by the excitation end line through the electromagnetic interconnection device is used as the intermediate equivalent power supply for the target line loop transfer. A closed-loop equivalent impedance model is established for the target line, and the closed-loop current is calculated. The closed-loop current is obtained by superimposing the closed-loop current component caused by voltage difference and the closed-loop current component caused by load transfer. Establish a discrete compensation voltage vector diagram formed by the combination of secondary winding taps, and select the optimal tap position based on the distance between the target compensation voltage and each discrete compensation voltage point; Candidate switching sequence schemes for the line are constructed, and tap position matching, loop current prediction, power transfer and load transfer calculations are performed on the candidate switching sequence schemes to obtain the evaluation results of each candidate switching sequence scheme. A comprehensive evaluation index is established based on the maximum loop closing current throughout the entire process, the total current stress of each major loop closing process, and the maximum voltage deviation throughout the entire process. The switching action sequence with the optimal comprehensive evaluation index is selected as the optimal switching sequence. Perform the target line loop closing, power transfer, and original power supply disconnection operations according to the optimal switching sequence to complete the distribution network loop closing and power transfer.

2. The method according to claim 1, characterized in that, When line A is the excitation terminal and line X is the target line, the equivalent voltage at point O is expressed as: Among them, U A Let T be the three-phase voltage vector of excitation terminal line A. AX U is the equivalent transformation matrix for the multi-terminal electromagnetic interconnection from line A to the target line X. O (X) This is the equivalent voltage vector at point O facing the target line X.

3. The method according to claim 1, characterized in that, Any phase of the target line X The closed-loop current is expressed as: ;in, The loop current component is caused by the difference between the equivalent voltage at point O and the target line voltage. Let be the closed-loop current component caused by the load transfer of the target line; where, For point O facing the target line X Equivalent voltage, For the target line X Phase original voltage, superscript Z represents the conjugate operation. AO, Z is the equivalent impedance of the path from the excitation terminal to point O. OX, λ is the equivalent impedance from point O to the target line access point. X, S is the load transfer ratio coefficient for the target line. LX, The target line load power.

4. The method according to claim 1, characterized in that, The discrete compensation voltage vector diagram is formed by combining the taps of the secondary winding, constituting multiple discrete compensation voltage points. The set of compensation voltages is defined as follows: Where N is the number of discrete points of the compensation voltage; Let the target compensation voltage be expressed as U in a rectangular coordinate system. ref =(U x U y The discrete compensation voltage point corresponding to the k-th tap is represented as U. c,k =(U cx,k U cy,k If the target compensation voltage is such that the distance between the target compensation voltage and the discrete compensation voltage point of the tap is defined as: ； Select the one that satisfies The tap position is taken as the current optimal tap, where U x U y U represents the real and imaginary parts of the target compensation voltage, respectively. cx,k U cy,k These are the real and imaginary parts of the k-th discrete compensation voltage point, respectively; When the target compensation voltage falls into a diamond-shaped region of the discrete voltage graph, minimum distance selection is performed only among the adjacent taps in the diamond-shaped region.

5. The method according to claim 1, characterized in that, To avoid a situation where three power sources are simultaneously supplying power during the power transfer process, the operation schemes with switching sequences CBA and BCA are first eliminated, and the remaining candidate switching sequence schemes are defined as follows: S1: ABC means that line A first builds up voltage at point O, then connects to line B and completes the load transfer on the B side, and then connects to line C and completes the load transfer on the C side. S2: ACB indicates that line A first establishes voltage at point O, then connects to line C and completes the load transfer on the line C side, and then connects to line B and completes the load transfer on the line B side. S3: BAC, indicating that line B first establishes voltage at point O, then connects to line A and completes the load transfer on the line A side, and then connects to line C and completes the load transfer on the line C side; S4: CAB indicates that line C first establishes voltage at point O, then connects to line A and completes the load transfer on the line A side, and then connects to line B and completes the load transfer on the line B side.

6. The method according to claim 1, characterized in that, The multi-terminal electromagnetic interconnection device is a single three-terminal electromagnetic interconnection device, including a first winding, a second winding, and a third winding arranged on the same magnetic circuit, wherein: the first winding is connected to port A of line; the second winding is connected to port B of line; and the third winding is connected to port C of line; at least two of the first winding, the second winding, and the third winding are provided with adjustable taps, which are used to adjust the equivalent voltage at point O and the compensation voltage on the target line side by changing the equivalent turns ratio of the corresponding port winding.

7. The method according to claim 6, characterized in that: When the candidate switch sequence is S1:ABC, the loop-closing and power transfer process includes the following steps: First close switch K A An equivalent voltage is established at point O via the first winding of the multi-terminal electromagnetic interconnection device through line A; based on the difference between the equivalent voltage at point O and the equivalent voltage on the B side, the tap position of the second winding of the multi-terminal electromagnetic interconnection device is selected, and switch K is closed under the condition that the predicted loop current meets the limit. B After both KA and KB are closed, the first and second winding taps of the multi-terminal electromagnetic interconnection device are adjusted together to make the load L of line B... B The power supply will be gradually transferred from the original power source of line B to the power source of line A. When the power and current at the source end of line B drop to within the preset threshold, disconnect the original power supply to line B. After the original power supply on line B is disconnected, the tap position of the third winding of the multi-terminal electromagnetic interconnection device is selected based on the difference between the current equivalent voltage at point O and the equivalent voltage on line C, and the switch K is closed under the condition that the predicted loop current meets the limit. C ; By jointly adjusting the first and third winding taps of the multi-terminal electromagnetic interconnection device, the load L of line C is adjusted. C The power supply will be gradually transferred from the original power source of line C to the power source of line A. Once the power and current at the source end of line C drop below a preset threshold, disconnect the original power supply to line C.

8. The method according to claim 7, characterized in that: The joint adjustment of the first and second winding taps of the multi-terminal electromagnetic interconnection device causes the load L of line B to be adjusted. B The gradual transfer of power from the original power source of line B to line A is achieved by adjusting the phase angle difference and amplitude difference between the equivalent voltages on the line A side and the line B side; let the equivalent voltages on the line A side and the line B side after transformation by the multi-terminal electromagnetic interconnection device be as follows: Among them, T A and T B These are the tap positions of the first and second windings of the multi-terminal electromagnetic interconnection device, respectively. The phase angle difference between the equivalent voltages on both sides of line A and line B is: ;in, Let be the phase angle of the equivalent voltage on side A of the line. The phase angle is the equivalent voltage on side B of the line; The equivalent reactance of channel AB is X. AB Under the condition of [condition], the active power transferred from line A to line B and reactive power Approximately satisfies: ； ； By adjusting δ AB By controlling the direction and magnitude of active power transfer, and adjusting the difference in equivalent voltage amplitude between lines A and B, reactive power and voltage support are controlled, thereby achieving the load L of line B. B Smooth power transfer from the original power source of line B to line A; For the power transfer of line C, let the equivalent voltage on side A and the equivalent voltage on side C after transformation by the multi-terminal electromagnetic interconnection device be respectively: Among them, T A and T C These are the tap positions of the first and third windings of the multi-terminal electromagnetic interconnection device, respectively. The phase angle difference between the equivalent voltages on both sides of line A and line C is: ;in, Let be the phase angle of the equivalent voltage on side A of the line. The phase angle is the equivalent voltage on side C of the line; The equivalent reactance of the AC channel is X. AC Under the condition of [condition], the active power transferred from line A to line C and reactive power Approximately satisfies: ； ； This achieves the load L of line C. C The power supply is smoothly transferred from the original power source of line C to line A.

9. The method according to claim 8, characterized in that: The load L of line B is determined when at least one of the following conditions is met at the original power supply outlet of line B. B The transfer of power from the original power source of line B to line A has been completed: Among them, P SB and I SB These represent the output power and current of the original power supply for line B, respectively, N. B For the set of key monitoring nodes on side B of the line, ε P ε I and ε U These are the allowable power, current, and voltage deviation thresholds, respectively. The actual voltage at node n; Let n be the reference voltage at node n; The load L of line C is determined when at least one of the following conditions is met at the original power supply outlet of line C. C The transfer of power from the original power source of line C to line A has been completed: Among them, P SC and I SC These represent the output power and current of the original power supply for line C, and N. C This is the set of key monitoring nodes on the C side of the line.

10. The method according to claim 5, characterized in that: The candidate switching sequence schemes S1, S2, S3 and S4 are calculated and evaluated respectively; when S3 or S4 is the candidate sequence, it is allowed to reverse excite the common magnetic circuit through the corresponding port winding of the multi-terminal electromagnetic interconnection device by line B or line C respectively, so as to establish an initial equivalent voltage at point O. For each candidate switch sequence scheme, its tap sequence, loop current trajectory, voltage deviation trajectory, and comprehensive evaluation values ​​FS1, FS2, FS3, and FS4 are calculated, and the optimal switch sequence is automatically selected based on the principle of minimizing the comprehensive evaluation value.

11. The method according to claim 10, characterized in that: The comprehensive evaluation value of any candidate switching sequence scheme m is constructed as follows: Maximum loop closing current throughout the entire process ; Total current stress during each major loop closure process ; Maximum voltage deviation throughout the process ; After normalization, we get: ; in, For the entire process time, The number of main loop closure processes, and The first The start and end times of the transient duration interval of the secondary major loop closure. It is a set of key monitoring nodes throughout the entire process. Let ω1, ω2, and ω3 be the reference voltage at node n, and let ω1, ω2, and ω3 be weighting coefficients that satisfy ω1 + ω2 + ω3 = 1. Let ω1, ω2, and ω3 be weighting coefficients that satisfy ω1 + ω2 + ω3 = 1. The candidate switching sequence schemes are selected as the optimal switching sequence.

12. An electronic device, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the distribution network loop-connection method based on a multi-terminal electromagnetic interconnection device as described in any one of claims 1 to 11.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the distribution network loop transfer method based on a multi-terminal electromagnetic interconnection device as described in any one of claims 1 to 11.

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